The present invention relates to endoscopic surgical instruments. More particularly, it relates to a new and improved bipolar electrocautery snare for use with such instruments.
Endoscopic surgical instruments such as bronchoscopes, colonoscopes, gastroscopes, sigmoidoscopes, and the like, are widely used at present by the medical profession. An endoscope generally comprises a tube or cannula containing a variety of instruments. The endoscope is inserted through an orifice into a body organ such as the lungs, bladder or prostate, or a body cavity, such as the intestines. More particularly, endoscopes are usually provided with an optical observation system which includes for example a lamp, an objective lens, an image guide formed of a flexible bundle of optical fibers and an eyepiece, which enables a surgeon to visually examine the internal environment surrounding the inserted end of the endoscope. Fluid conveying tubes are also provided within the endoscope for delivery of irrigation fluid to and withdrawal of blood and other fluids from the surgical area located adjacent to the end of the tube. An instrument channel is provided to slidably receive a surgical instrument, such as a cutting surgical electrode in the form of a loop or snare. The surgical snare may be extended or withdrawn from the end of the endoscope and can be made to surround any undesirable growth within the body organ or cavity. The snare is electrically connected to a high frequency electric current source which when activated passes a high frequency current through the loop which cauterizes the tissue growth within its grasp.
The development of endoscopy has provided great improvements in the surgical arts. In bowel surgery for instance, the surgeon is now able to get a close up view of lesions or growths, to perform biopsies for testing, or remove growths entirely, without the need to perform a laparotomy. The patient may thereby forgo certain life-threatening risks, such as sepsis, associated with that particular surgical procedure.
Surgical electrocautery snares for use with endoscopes are described, for example in U.S. Pat. No. 2,484,059 and U.S. Pat. No. 3,995,578. Typically, and as described therein, the surgical snare is formed of a flexible resilient stainless steel wire which is specially shaped to form an expandable loop as it is extended from an electrically insulated sheath. As the snare is pulled back into its sheath, the diameter of the loop gradually decreases. The ends of the snare loop are electrically connected to a flexible conductive wire extending within the protective sheath which is in turn electrically connected to one terminal of a high frequency electrocautery frequency source. The patient is grounded or otherwise connected to the other terminal of the high frequency source. To resect a growth, such as a polyp or tumor extending from an otherwise healthy tissue wall, the snare is positioned around the base of the growth and tightened to gather the tissue at the point of attachment of growth to tissue wall.
With the snare in position, the high frequency current generator is activated causing the flow of electrocauterizing current to pass from the loop to the tissue at the point of contact and then through the patient's body to ground. The snare is tightened as the current is applied until complete removal of the growth is achieved. One advantage of this type of surgery is that it is relatively bloodless because the snare electrode cauterizes the tissue as it cuts through it. A serious shortcoming of such snares is that they are unipolar. Current must pass from the snare loop through the patient's body to ground and aberrant or stray return currents, not localized to the point of attachment of the growth have been observed. These aberrant return currents can cause burns and discomfort to the patient and unintentional cauterization of healthy tissue, all of which are extremely undesirable.
Although presently available unipolar snares are serviceable in experienced hands, situations frequently arise in which surgeons desire a greater degree of control over the extent of tissue being cauterized. In order to better illustrate the problem, a schematic drawing of the unipolar electrocautery procedure is provided in FIG. 1. As illustrated therein, current flows from the electrocautery current generator to an active electrode. The current then must propagate through the entire volume of tissue in order to return to the ground plate and back to the other terminal of the generator. A partial limitation of the extent of tissue cauterized is provided because the current density at the small active electrode is much greater than the current density at the large ground plate, even though the same total amount of current that leaves the active electrode must return through the ground plate. The localization, however, is imperfect and is often not as precise as desired.
Bipolar electrocautery is a well-recognized method for overcoming the limitations of unipolar electrocautery. As schematically depicted in FIG. 2, bipolar electrocautery involves the use of two active electrodes. In this bipolar procedure current travels from the generator to one active electrode and returns via the second active electrode. In this procedure the current path lies largely in the small volume of tissue around the two electrodes. Although some slight spreading of current effect may occur, the effective radius of cauterization is far less than with the unipolar method.
Bipolar electrocautery is of considerable benefit in area where close control of the amount of tissue being cauterized is essential. Hertofore it has found wide application in the field of neurosurgery. However, in endoscopic surgery it is also very important to have precise control over the amount of tissue being cauterized. More particularly, during endoscopic removal of growths in the intestines, precise control of the amount of cauterization would be helpful in minimizing the risk of perforation of the intestinal wall. This is especially true in the colon, where the incidence of growths requiring removal is quite high and for which the intestinal wall is quite thin.
It has generally been believed that if the advantages of bipolar electrocautery could be applied to endoscopic surgery, a substantial safety margin for these surgical procedures could be provided. However, a bipolar electrocautery surgical snare for use with endoscopes has remained unavailable.
Accordingly, it is an object of the subject invention to provide a new and improved electrosurgical snare which is bipolar.
It is another object of the subject invention to provide a bipolar surgical snare which permits endoscopic electrocauterization of growths within the body of a surgical patient with precision and accuracy.
It is a further object of the subject invention to provide a bipolar electrosurgical snare which allows for the endoscopic removal of growths with reduced or eliminated risk to both the patient and surgeon of injury from aberrant or stray return currents.